CHICAGO – Girls as young as 12 were lured into prostitution — coerced with brutal beatings and death threats – as part of a coordinated sex trafficking operation by Chicago gang members, authorities alleged Wednesday in announcing a rare undercover investigation that relied on wire taps.

The ongoing 18-month probe was conducted under provisions of the Illinois Safe Children's Act, which was signed into law last year. It allows wire taps and treats minors arrested for prostitution as victims instead of criminals. While Illinois is not the first to have such legislation, it is among the first states to rely on wire taps in a sex trafficking investigation.

Nine people, all from the Chicago area, were charged in the investigation and dozens of girls and young women have been taken off the streets and placed with social service agencies, said Cook County State's Attorney Anita Alvarez.

"This is a business for them," she said. "It's a crisis that occurs in our very city. It's often hidden in plain sight."

According to authorities, the girls and young women were recruited from mostly public places — outside schools, from El trains or malls — and forced to work. They were threatened with death or harm to their families. One woman was cut on her face with a broken bottle so she would become disfigured and others were forced into car trunks and driven around for extended periods of time in a torture process called "trunking."

"It pulls at your heartstrings when such young girls are exploited in such a fashion," said Chicago Police Superintendent Garry McCarthy, whose agency cooperated on the investigation.

The alleged gang members — all charged with involuntary sexual servitude of a minor, among other things — preyed on girls and women who came from poverty, broken homes or had drug abuse problems, authorities said. They used the streets and the Internet to set up the transactions, with one girl earning up to $3,000 a day for the operation. Gang members would sell the girls to other gangs — some of them loosely connected — sometimes for a mere $100, Alvarez said.

"These girls make money, but they don't see it," Alvarez said.

The operation, dubbed "Little Girl Lost," largely took place on the city's west and south sides. In street level operations, Chicago police and Cook County Sheriff's Police arrested more than 50 customers and seized nearly 40 vehicles in the investigation.

Authorities used the court-ordered wire taps as they would in drug trafficking cases: to listen in on cell and landline phone conversations. Several conversations between the alleged gang members — laced with profanity and detailed plans for beatings — are transcribed in court documents.

Around two dozen states have laws on the books that allow wire-taps in sex-trafficking cases, but it's unclear how many states have used them, said Mary Ellison, a director of policy for the Polaris Project, a Washington, D.C.-based non-profit group.

"It's a newer practice to use wire-tapping laws," she said. "It's a very effective tool and we'd like to see it more."

For one, it means that authorities don't have to rely on the testimony of prostitutions against their pimps, Alvarez said. She anticipated more arrests over the coming months.

At least 16,000 girls and women are involved in Chicago's commercial sex trade on any given day, according to federal authorities and experts.

Illinois' new law, which also increases penalties for those charged and allows for seizure of vehicles, essentially decriminalizes prostitution for minors, by literally removing "juvenile prostitutes" from the criminal code. Minor girls are placed in child protective services instead of the criminal system. A handful of states have similar laws advocating for victims including New York, Washington and Minnesota.

Authorities added, though, that there have been some success stories because of the operation.

The girls recovered from the investigation — their names weren't released publicly — have been getting counseling and several have even been able to graduate, some of them from the eighth grade.

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